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From "Wangda Tan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-7149) Cross-queue preemption sometimes starves an underserved queue
Date Thu, 07 Sep 2017 16:45:00 GMT

    [ https://issues.apache.org/jira/browse/YARN-7149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16157212#comment-16157212
] 

Wangda Tan commented on YARN-7149:
----------------------------------

And the other place we need to change is: {{LQ#getTotalPendingResourcesConsideringUserLimit}}.

Instead of do a strict headroom: {{headroom = userLimitResource - user.used}}
We should relax this computation as well. We should give at least one container when headroom
>= 0. Otherwise it makes preemption logic inconsistent to allocation logic.

> Cross-queue preemption sometimes starves an underserved queue
> -------------------------------------------------------------
>
>                 Key: YARN-7149
>                 URL: https://issues.apache.org/jira/browse/YARN-7149
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacity scheduler
>    Affects Versions: 2.9.0, 3.0.0-alpha3
>            Reporter: Eric Payne
>            Assignee: Eric Payne
>         Attachments: YARN-7149.demo.unit-test.patch
>
>
> In branch 2 and trunk, I am consistently seeing some use cases where cross-queue preemption
does not happen when it should. I do not see this in branch-2.8.
> Use Case:
> | | *Size* | *Minimum Container Size* |
> |MyCluster | 20 GB | 0.5 GB |
> | *Queue Name* | *Capacity* | *Absolute Capacity* | *Minimum User Limit Percent (MULP)*
| *User Limit Factor (ULF)* |
> |Q1 | 50% = 10 GB | 100% = 20 GB | 10% = 1 GB | 2.0 |
> |Q2 | 50% = 10 GB | 100% = 20 GB | 10% = 1 GB | 2.0 |
> - {{User1}} launches {{App1}} in {{Q1}} and consumes all resources (20 GB)
> - {{User2}} launches {{App2}} in {{Q2}} and requests 10 GB
> - _Note: containers are 0.5 GB._
> - Preemption monitor kills 2 containers (equals 1 GB) from {{App1}} in {{Q1}}.
> - Capacity Scheduler assigns 2 containers (equals 1 GB) to {{App2}} in {{Q2}}.
> - _No more containers are ever preempted, even though {{Q2}} is far underserved_



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